In an equalization method used in the receiver of a multiple input multiple output system, in which spatial multiplexing is performed, raising tremendously achieved bit rate while using reasonable supplementary resources, the detection and decoding, of the transmitted signal, at the receiver side, may be delicate, because of the mixing altogether of the signals transmitted by the different spatial layers of the multiple input multiple output system.
According to a first prior art, which deals with turbo equalization technique and which will be more detailed later with respect to FIG. 1, it is known to use a feedback signal from channel decoding to equalization in order to also use extrinsic information as for example the redundancy bits, and not only use the intrinsic information which is the information content of transmitted signal. An advantage of this first prior art is to exploit all available information to improve decoding, including information coming from the structure of the coding technique such as for example the redundancy bits. A drawback of this first prior art is that, for high bit rates using sophisticated modulation techniques such as complex constellations of coding symbols, the number of leaves in the search trees rapidly becomes very high and the way to process these leaves rather complex. Therefore, the needed resources to implement such a decoding technique soon become too important.
According to a second prior art, which deals with sphere decoding in equalization technique, it is known to build a search tree which is processed as well as shrunk during processing, to decode transmitted signals. An advantage of this second prior art is the efficiency to prune the search tree rapidly, which could otherwise become rapidly too big, having too many leaves to be processed. However, a drawback of this second prior art is that it uses only part of available information, since only the intrinsic information which is the information content of transmitted signal is analyzed and used, but not the extrinsic information which is the other available information coming from the structure of the coding technique as for example the redundancy bits. Examples of this second prior art are a first article [O. Paker, S. Eckert, A. Bury, “A Low Cost Multi-standard Near-Optimal Soft-Output Sphere Decoder: Algorithm and Architecture, IEEE DATE 2010], a second article [C. P. Schnorr, M. Euchner, “Lattice basis reduction: Improved practical algorithms and solving subset problems” Math. Programm., vol. 66, pp. 181-191, 1994], a third article [Studer, C.; Wenk, M.; Burg, A.; Bolcskei, FL “Soft-Output Sphere Decoding: Performance and Implementation Aspects” Fortieth Asilomar Conference on Computing and Processing, 2006].
According to a third prior art, for example disclosed in European patent application EP 2448205, it is known to make some approximation within the search tree used in sphere decoding in equalization technique to lower needed decoding time and resources. An advantage of this third prior art is to lower needed decoding time and resources, thanks to the made approximation. A drawback of this third prior art is that the made approximation can only be used with classical sphere decoding, and cannot be implemented when using other available information than the information content of the transmitted signal, like a priori information used in turbo equalization.
All these prior art techniques present a drawback, either they do not use all available information and therefore the efficiency of decoding is somewhat poor, or they need too much time and resources to be implemented.